There are multiple options that you can use, and it's really going to come down to personal preference.
The script idea would work, and depending onthe frequency of use may be your best bet. A simple ctrl+shift+s will pull the script manager up.
Another solution could be to create a hidden layout with a single field to enter the journal data.
Another one would be to create a whole table dedicated to bug tracking to let you keep each bug/mod/addition separate for easy viewing. Just just throw the a portal on a hidden layout to view/add to it. This option would be my preference. It should only take 5 minutes to setup, and it'll be more organized than the other methods.
If it's not at the deployment stage, I make "notes" on the layout I'm altering. And I heavily comment my scripts! These help while in development. Removing the "notes" for development, doesn't "log" them, however. Yes, create a new table or separate file and with the use of container fields, you can add screenshots. Only you (and other developers would have access to this table.
Personally, I would love to see the notes of other developers to see what kind of changes were made - especially if multiple developers have their hands on it.
I use a script trigger or custom menu set ( Developer Menu ) to have a shortcut to open a separate window or dialog where I can enter notes as I work. Since it is only available on the menu set, and that set is only installed when I log in...it's very handy.
It picks up the Table name, Table Occurrence, Layout Name, etc. It all pulls in from a custom function, that I believe I picek up from Matt Petrowsky.